Smartphone gives bikes an automatic gearbox

I AM just about to change gear on a racing bike when something rather marvellous happens: it switches to the right one of its own accord. I pedal harder and it happens again - just as if this bike is tuned to how I want to cycle. And in fact, it is: I'm testing the first bicycle gearbox that is both automatic and wireless.

The system, developed by Mark Wilson and colleagues at Cambridge Consultants in the UK, uses your smartphone to calculate the best gear to be in for the current pedalling speed, then wirelessly shifts up or down.

It also uses the phone's accelerometer to know when to change down in an emergency stop. Although there's a noisy crunch of gears as it clicks down a few cogs in one go, it means you can pull away afterwards with ease. The system will eventually be able to anticipate what gear you need, if you are approaching a hill, for instance, by using the phone's GPS capability.

Mechanical automatic gearboxes already exist, but they wear out quickly as they are based on moving flywheels. The wireless method activates an electric gear shift that has no such issues. What's more, because it operates via a smartphone, serious cyclists can use it to analyse performance.

An electric gear shift is normally connected via a cable to a lithium battery and gear switches on the handlebars. "We've cut the cables between the switches and the gears and replaced them with a smart, low-energy version of Bluetooth designed for very long battery life," says team member Tim Fowler.

In manual mode, Bluetooth on the gear shift communicates with the rider's iPhone, and an app on that phone relays the rider's commands as they are tapped into the phone during the ride.

In automatic mode, a magnetic sensor on the main crank tells the app your pedalling speed - known as cadence - while a wheel sensor tells it your road speed. The app then computes the correct gear and beams it to the gear shift.

For the last two months, the team has been testing the system on a treadmill. "Our tester tells us he never feels like he is in the wrong gear," says Wilson. The next step is to integrate GPS to enable the app to switch to a lower gear if the bike is approaching a hill.

Joel Natale, head buyer at Evans Cycles, which runs 50 UK cycle shops, says that it is unlikely that many riders will want to abandon manual gear changing. "However, there is one group for whom this may make total sense, and that's triathlon riders - who like to ride at constant cadence and power," he says.

Next, the Cambridge team wants to develop a bike version of anti-lock braking, with the phone controlling the brakes to prevent a skid. "A front wheel lock is generally catastrophic. This may help," says Wilson.

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